Baby, It’s Cold Outside

A winter population of butterflies is really hard to upkeep, especially after several nights of freezing temperatures. There are fewer butterflies in the Flight Encounter and those that remain will not fly until the temperature rises. They will remain all day, stock still on the same leaf or flower if the temperature remains too low.

Sort of Cold Blooded: Surviving over winter is tough for butterflies since they are poikilotherms (of varying temperature) and are very much subject to outdoor temperatures. Butterflies and moths have some small ways they can help control their temperature like shivering their flight muscles to provide some warmth, but they are still very much subject to cold temperatures which make them sluggish or torpid.

Butterflies bask in sunlight and allow the solar radiation to warm the haemolymph (circulatory fluid of certain invertebrates) that runs through the veins in their wings, basically using their wings like solar panels. Basking with the addition of shivering can raise the temperature of a monarch so that it can fly even though external temperatures might be prohibitive.

The article Thoracic temperature, shivering, and flight in the monarch butterfly, Danaus plexippus (L.) from The Journal of Comparative Physiology (April, 1970) showed that a monarch butterfly shivering its wings at 59 to 60 degrees Celsius could raise its temperature at 1.3 degrees Celsius/minute reaching a thoratic temperature of 4 degrees Celsius greater than ambient temperature. At higher temperatures the butterflies could warm themselves faster and to an even greater temperature above ambient.

Let’s Get Away: Some butterflies will migrate to warmer areas in the winter, like the well described migration of monarchs to forests of Mexico. Here in peninsular Florida we are a winter destination for several species of butterflies. The Gulf Fritillary and Long Tailed Skipper overwinter in southern Florida and the Buckeye and Cloudless Sulphur migrate to southeastern states for the duration of the cold season. These butterflies may overwinter as adults using man-made or natural crevice type structures in which to hibernate and shelter.

Several years ago I attended a butterfly field lecture in Gainesville given by Dr. Jaret Daniels. During the course of the walk our group saw hundreds of Gulf Fritillary butterflies flying south along a power line cut near the San Felasco Hammock Preserve State Park. The butterflies flew fairly low to the ground and occasionally stopped for nectaring but they all continued on to points south and did not linger in north Florida.

Diapause: Some butterflies in various stages of development utilize diapause to overwinter. Diapause is a state of dormancy in which all development is suspended. Unlike hibernation where development and metabolism still occur at a slower rate, during diapause all cellular growth stops causing complete dormancy.

Triggered by a number of factors including length of daylight hours, temperature and possibly even the angle of sunlight which may indicate the approach of unfavorable conditions a butterfly may enter into the state of diapause.

A pupa entering diapause will cease development and the metamorphosis of the insect inside will halt until conditions become more favorable to the survival of the insect. The only energy used upkeeps the integrity of cells from breaking down, but does not cause cells to change, reproduce, or grow. A caterpillar in diapause will cease eating, growing, shedding or burning food-fuel that has been stored. They basically just stop.

Diapause is a true suspended animation. Check out more on diapause: Diapause research foundation and Longest Diapause among insects from IFAS